The main purpose of a Neutral Grounding Resistor (NGR) is to limit the fault current present in a single line to ground fault.  Limiting the possible current that can flow in such an event not only reduces damage to equipment but also helps safeguard personnel in the vicinity.  Depending on the design of the resistor, this current value can be either high or low, continuous or of a predetermined duration.  The resistor’s designed maximum current allows relays and protection settings to be easily determined and enacted, creating a safe work environment.


Resistance Grounding Comparison Chart – Standard Practices For Industrial Plants

600 volts and lower
2.4 to 35 kv

Grounding Method
Solid Grounding & High-Resistance Grounding
Low Resistance Grounding

Comparative Benchmarks for Various Grounding Methods
Methods of Grounding
Characteristics Ungrounded Solid Grounded Low Resistance High Resistance
Immunity to transient over-voltages Worst Good Good Best
Increase in voltage stress under line-to-ground fault conditions Poor Best Good Poor
Equipment protected against arc fault damage Worst Poor Better Best
Safety to personal Worst Better Good Best
Service reliability Worst Good Better Best
Maintenance cost Worst Good Better Best
Continued production after first ground fault Better Poor Poor Best
Ease of locating first ground fault Worst Good Better Best
Permits designer to coordinate protective devices Not Possible Good Better Best
Ground fault protection can be added easily Worst Good Better Best
Two voltage levels on the same system Not Possible Best Not Possible Not Possible
Reduction in frequency of faults Worst Better Good Best
First high ground fault current flows over grounding circuit Best Worst Good Better
Potential flashover to ground Poor Worst Good Best



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